A basic requirement of photography is that the camera always has to be kept level.
Levellable ball and socket heads have been well known to photographers for a long time. As opposed to conventional ball and socket heads that have three degrees of freedom, here two balls are mounted inside each other. The outer, larger ball is adapted for levelling the system, while the inner, smaller one is restricted to two degrees of freedom, thereby functioning as a bidirectional tilting head, which is the most frequently applied camera mounting and orienting solution in photography and videography.
This conventional solution has the drawback that, when the camera is tilted forward or backward from its centre position, its centre of gravity is displaced from above the centre of the ball, and is thereby displaced from its balance position and becomes tilted forward. To prevent that from happening, the user must pay constant attention.
The prior art patent application P 01 03299 discloses a ball and socket joint and embedding ring wherein the embedding ring receives a spherical body, and wherein the joint comprises a housing encompassing the embedding ring, with the embedding ring completely encompassing the spherical body along a section adjacent a great circle thereof. The embedding ring has a first inner rim and a second inner, each of the rims defining a respective surface dimensioned differently from the other one.
The patent application P 13 00365 discloses a ball and socket mounting device for equipment requiring to be levelled and rotated, particularly for mounting cameras on tripods. The solution comprises a housing, open at the top, having an inner spherical surface, a shell, open at the top, adapted for being rotated in the housing and having an outer spherical surface region corresponding in shape to the inner spherical surface of the housing, and a ball having a surface shape corresponding to the inner spherical surface of the shell and adapted to be rotatable with respect to the shell. A mounting disc, extending through the upper opening of the housing and either joined to or made integral with the ball, is connected to the ball. The essential feature of this solution is that the shell is a spherical shell with a centre angle greater than 180°, preferably 190°-210° that is open at the top, where the shell is covered at the top by a flat surface, and where the ball is arranged to be secured to the shell.
The above described solutions have the disadvantages that they do not prevent the body (camera) mounted on the ball and socket mounting device from tilting downward when the mounting device is displaced from its balance position, and, due to the application of the fastening mechanism the optical axis is slightly displaced during fixing the position of the inner ball, and furthermore, due to its configuration, the slit formed in the inner ball structurally weakens the neck portion of the inner ball, and thus decreases the stability of the mounting.
The disadvantages of the solution according to the patent application P1300365 are explained with the help of FIG. 20.
In the known solution a slit opening towards the mounting disc 2a is formed in the inner ball 5, which results in that only one of the halves of the neck portion of the inner ball 5—the neck portion 10a—is secured to the mounting disc 2a, which causes the optical axis to get displaced with respect to the adjusted plane. Thereby the precision adjustment of the optical system becomes unfeasible.
In addition to that, the camera 4 mounted on the mounting disc 2a cannot be kept balanced, and thereby the camera 4 becomes tilted with respect to the horizontal plane at an angle Ω.